If you have a fever or any other symptoms of COVID-19 or if you have received instructions from Public Health to self-isolate because of COVID-19, you must postpone getting vaccinated.


The following COVID-19 messenger RNA vaccines are currently available in Québec:

  • The Pfizer vaccine, approved for people 12 years of age and older;
  • The Moderna vaccine, approved for people 12 years of age and older.

Although the Moderna vaccine is authorized in Canada for people 12 years of age and older, the Quebec immunization committee (CIQ) recommends preferential use of the Pfizer vaccine for youth aged 12 to 17, as it may present a lower risk of pericarditis and myocarditis.

Where to get vaccinated
Go to the COVID-19 vaccination campaign page to find out the procedure for getting vaccinated.

How the vaccine works and ingredients

Vaccination prepares your body to defend itself against any microbes it may encounter.

The virus that causes COVID-19 is composed of a strand of genetic material, RNA (ribonucleic acid), surrounded by an envelope. On the surface of the virus, there are proteins, including the S protein (spike protein) which gives it its crown shape, hence its name coronavirus. The S protein allows the virus to infect cells in the human body.

COVID-19 messenger RNA vaccines block the S protein, preventing the virus from entering and infecting human cells.

The Pfizer vaccine contains:

  • messenger RNA;
  • lipids (ALC-0315 = ((4-hydroxybutyl)azanediyl)bis(hexane-6,1-diyl)bis(2-hexyldecanoate), ALC-0159 = 2-[(polyethylene glycol)-2000]-N,N-ditetradecylacetamide, 1,2-Distearoyl-sn-glycero-3-phosphocholine and cholesterol);
  • salts (potassium chloride, dibasic sodium phosphate dihydrate, sodium chloride, monobasic potassium phosphate
  • sugar (sucrose).

The Moderna vaccine contains:

  • messenger RNA;
  • lipids (1,2-distearoyl-sn-glycero-3-phosphocholine, SM-102, polyethyleneglycol-2000 DMG (1,2-dimyristoyl-rac-glycerol, methoxy-polyethylene glycol) and cholesterol);
  • solvents (trometamol, trometamol hydrochloride, acetic acid, sodium acetate trihydrate);
  • sugar (sucrose).

Number of doses

Two doses of COVID-19 messenger RNA vaccine are required for people in good health. Both doses are administered intramuscularly. The 2nd dose is needed for long-term protection.

For people with a weakened immune system or on dialysis, three doses are necessary. For further information, see the Additional dose of COVID-19 vaccine page.

People who received a viral vector-based vaccine (AstraZeneca or Covishield) for the 1st dose could receive a messenger RNA vaccine for their 2nd dose. Go to the Second dose of COVID-19 vaccine page for more information.

People who have had COVID-19 before receiving the vaccine only need 1 dose. For more information, see Vaccination for people who have had COVID-19 on the COVID-19 vaccination page.

Interchangeability of vaccines

The Pfizer and Moderna vaccines are similar in terms of how they work and their ingredients. Comité sur l'immunisation du Québec (CIQ) considers the 2 vaccines interchangeable. People given a different vaccine for their 2nd dose should be just as well protected as those who get the same one.

Based on the available data on vaccine interchangeability, it is recommended that the same vaccine be used for the 2nd dose if it is readily available at the vaccination clinic. However, the CIQ states that when administering the 2nd dose, if the messenger RNA vaccine used in the 1st dose is not readily available, a person may receive a different messenger RNA vaccine.

The messenger RNA vaccines are considered interchangeable and both doses received are considered valid.

Vaccine efficacy

The vaccine is thought to be over 90% effective after two doses. For young people, disease-prevention efficacy is 100% after 2 doses. The 2nd dose is needed to further reduce the virus’s ability to spread, extend the period of immunity, and improve the vaccine’s effectiveness, particularly against certain variants.

Efficacy after two doses of the messenger RNA vaccine in preventing disease caused by the Delta variant is around 90%, compared  96% in preventing hospitalizations.

Vaccine safety

See the Vaccine safety section on the COVID-19 vaccination page.

Symptoms after vaccination

Vaccination may cause symptoms such as redness at the injection site. Other problems may arise by chance and are unrelated to vaccination, such as a cold or gastroenteritis.

Most reactions are mild and short-lived. Local reactions may occur up to 8 days after vaccination. Reactions are less common in people over 55 years of age.

In a minority of people, the vaccine-induced reactions that prevent you from doing your daily activities for one or two days may occur. Reactions typically include fatigue, headache and muscle or joint pain. These reactions are less common in older adults. They are slightly more frequent after the 2nd dose.

The vaccines cannot cause COVID-19 because they do not contain the SARS-CoV-2 virus responsible for the disease. However, a person who has been in contact with the virus in the days prior to or following vaccination may still develop COVID-19. It is important to continue to follow the health instructions until most of the population has been vaccinated.

Nature and frequency of known reactions to these vaccines


Known reactions to these vaccines

In most cases
(more than 50% of people)

  • Pain at the injection site

Very often
(less than 50% of people)

  • Headache, fatigue*
  • Fever or chills
  • Joint pain
  • Muscle pain
  • Diarrhea, vomiting
  • Swollen lymph nodes in the armpits
(less than 10% of people)
  • Redness or swelling at the injection site**

(fewer than 1 in 1000 people)

  • Facial swelling
Very rarely (less than 1 person in 10,000)
  • Myocarditis or pericarditis in the days following vaccination

* The majority of young people age 12–15 experience fatigue or a headache.

** This reaction can appear more than a week after the vaccination.

Fatigue, headache, and muscle and joint pain occur more often after the 2nd dose.

Myocarditis or pericarditis occur more frequently in young males under the age of 30 in the days following the 2nd dose of COVID-19 messenger RNA vaccine. Cases present most often with mild symptoms and recover quickly.

Approximately 2 in 100 000 people may have a serious allergic reaction after being given an RNA-based vaccine. This reaction is more common than is usually expected after a vaccine, but is still very rare.

What to do after vaccination

Recommendations to follow in the minutes after vaccination

Wait 15 minutes before you leave the place where you were given the vaccine. If an allergic reaction occurs, the symptoms will appear a few minutes after you get vaccinated.

If you have side effects, tell the person who gave you the vaccine immediately. They can treat you there.

Recommendations to follow at home

If you experience redness, pain or swelling at the injection site, apply a cold damp compress.

If necessary, take pain or fever medication.

When to consult

Consult a doctor if any of the following apply to you:

  • You have serious or unusual symptoms.
  • You develop chest pain, palpitations or shortness of breath.
  • Your symptoms get worse instead of better.
  • Your symptoms last more than 48 hours.

If you have symptoms of COVID-19, use the COVID-19 Symptom Self-Assessment Tool to find out if you need to get tested.

Health instructions

The start of vaccination does not mean the end of health measures. It will take several months to protect a sufficiently large proportion of the population. It is essential to continue to follow the health instructions until further notice.

Why continue to protect yourselves after you’ve been vaccinated against COVID-19?